354 GAEY N. CALKINS 



SUMMARY OF OBSERVATIONS 



1. Subject Uroleptus mobilis, Engelmann, a ciliate belonging 

 to the family Oxytrichidae, order Hypotrichida of the Infusoria. 



2. Treatment. Description of species, pp. 293 to 296; tech- 

 nical methods, pp. 297 to 299; history of the nuclei during divi- 

 sion, pp. 299 to 307; during conjugation, pp. 308 to 332; com- 

 parisons with other ciliates, pp. 333 to 353. 



3. Macronuclei 8 in number. In preparation for cell division 

 these fuse to form one (pp. 299 to 301). Prior to division of the 

 cell this macronucleus divides twice; after division of the cell 

 these four divide once again to form 8 (pp. 301 to 303) . Divisions 

 are amitotic. 



4. Micronuclei variable in number from 2 to 6. They do not 

 fuse in preparation for cell division but the number is reduced to 

 2, probably by absorption (pp. 303 to 305). With cell division 

 the 2 nuclei divide. One of the 4 may degenerate or all may 

 divide. In latter case 2 degenerate while 6 divide to form 12, 

 6 for each daughter cell. Of these 6, one or two may degenerate 

 (pp. 306 to 307). Divisions are always mitotic with 8 single 

 or partially fused chromosomes. Whether chromosome division 

 is transverse or longitudinal could not be determined. 



5. Paedogamous conjugation lasts from 28 to 36 hours. The 

 macronuclei are retained throughout the process, but undergo 

 progressive granular disintegration (pp. 308 to 309). They are 

 finally absorbed in the protoplasm and have disappeared on the 

 fourth or fifth day after conjugation (pp. 309 to 310). 



6. Four micronuclei is the usual number in conjugants. All, 

 or a part of them only, form first maturation spindles. The pro- 

 phase stage for these is a characteristic nucleus termed the para- 

 chute nucleus, with an intranuclear division center (p. 313). The 

 massed chromatin disperses first as a dense reticulum; chromatin 

 collects at the nodes of this reticulum to form granules 24=1= in 

 number. Eight definite chromosomes may be formed by further 

 fusion (type 2) or the nuclei may divide without such fusion 

 (type 1), 12 =t granules going to each daughter nucleus (p. 314). 

 Whether division is transverse or longitudinal could not be deter- 

 mined (p. 315). 



